1. Field of the Invention
The present invention relates generally to shock absorbers, and more specifically, to shock absorbers having a composite base assembly with an over-molded closure insert.
2. Description of the Related Art
Conventional shock absorbers known in the related art typically include an outer tube, a piston assembly, a rod, fluid, and one or more valves, whereby the piston assembly is connected to the rod and travels within fluid in the outer tube in operation so as to dampen axial movement of the rod with respect to the outer tube. To that end, respective opposing ends of the rod and outer tube are attached to different members or structures so as to dampen movement therebetween. By way of example, conventional automotive suspension systems utilize shock absorbers in connection with springs to control the suspension damping in compression and rebound, whereby the shock absorber is typically attached to a knuckle supporting a wheel at one end, and to a portion of the vehicle's frame or body at the other end.
Depending on the application, the shock absorber may also include an inner tube disposed inside the outer tube, wherein the piston assembly is instead supported in the inner tube. The shock absorber is sealed at an end that receives the piston assembly. The inner tube defines a working chamber filled with fluid through which the piston assembly can move in operation. Similarly, a reservoir chamber is defined in the space between the outer tube and the inner tube. The reservoir chamber also contains fluid and is in regulated fluid communication with the working chamber via one or more valves. The chambers are sealed to prevent the leakage of fluid therefrom. The outer tube is typically manufactured from steel and, consequently, can be heavy. Since the outer tube is manufactured from steel, the end of the outer tube is sealed by known methods, such as crimping or roll forming. The outer tube typically engages a rod guide assembly to seal the chambers. In an effort to reduce the weight of the outer tube, thin-walled steel or aluminum may be used. However, it will be appreciated that reducing the wall thickness of the outer tube or using aluminum will reduce the weight, which can lead to reduced strength.
Composite materials have increasingly been used in automotive applications to reduce weight. Thus, given the drawbacks of outer tubes manufactured from steel discussed above, it is desirable to manufacture the outer tube from a composite material. However, it will be appreciated that composites have significantly different material properties than those of metals. Particularly, composite materials have a lower stiffness and therefore have greater elongation than metals. Another drawback is the need to seal the shock absorber in such a manner to prevent fluid from escaping and to be sufficiently strong to withstand the preloaded forces and the external forces.
Typically, shock absorbers are assembled with an internal preload between the inner tube and the outer tube, so as to prevent the various components discussed above from coming lose in operation, and to help keep the piston assembly, rod, inner tube, and outer tube aligned in operation. Proper alignment ensures reduced friction and low noise in operation. Thus, it will be appreciated that axial rebound loading of the shock absorber may cause a composite outer tube to deform significantly, such that the preload discussed above would disappear and the various components could come loose, leading to increased noise and friction as well as decreased performance and component life.
Moreover, it will be appreciated that the flexibility and elongation of composite materials inherently makes attachment with metal components or assemblies more difficult during manufacturing and can necessitate fastening or securing features that are complex and expensive to manufacture. Moreover, all-metal shock absorbers are manufactured with well established processes, such as roll forming or crimping, using existing machinery unsuitable for use with composites. These manufacturing lines are very costly to install and have been developed over many years of refinement and the prior art composite assemblies do not allow for closure with the existing processes.
Each of the components of a shock absorber of the type described above must cooperate to effectively dampen axial movement in operation. While shock absorbers known in the related art have generally performed well for their intended purpose, there remains a need in the art for a shock absorber that has superior operational characteristics, performs reliably, and provides advantages relating to decreased weight.